1. Field of the Invention
The present invention relates to a supersonic sensor head for a supersonic a non-destructive test apparatus for examining a test object without destroying the same.
2. Discussion of the Related Art
In a method for manufacturing articles such as machines and structures, plates manufactured by deformation processing are welded to each other. The stability of the welded parts is sometimes confirmed by the non-destructive test when the welded structures are required to have a particularly high reliability.
As an apparatus for the non-destructive test, a supersonic non-destructive test apparatus is known. When the supersonic non-destructive test apparatus is used, a vibrator in the apparatus for outputting and inputting supersonic waves, is pressed to an object to be tested (test object) via a contact medium. More specifically, there are two non-destructive test methods, i.e. wet-type and dry-type methods for testing test objects.
An example of the wet-type supersonic non-destructive test method is shown by a diagram in FIG. 5. As shown the figure, an upper plate 102 and a lower plate 103 are welded to each other by spot welding, so that a test object is formed. A welded part 104 a in the test object 101 is tested by the supersonic non-destructive test method for determining the quality. For this purpose, a nugget diameter D of the welded part 104 is determined, and the stability (soundness) of the welding is judged from the measurement result.
For determining the nugget diameter D in the wet-type supersonic non-destructive test method, a liquid contact medium 105 such as water or oil is applied to a surface of the upper plate 102. The contact medium 105 plays a role as a supersonic wave propagation material. A supersonic vibrator 106 is pressed to the test object 101 so that the upper plate 102 and the supersonic vibrator 106 closely contacts each other via a film made of the liquid contact medium 105 provided therebetween. Supersonic wave is transmitted from the supersonic vibrator 106, reflected in the test object, and received by the vibrator 106. Accordingly, the nugget diameter D is determined from the difference of the forwarded and returned supersonic waveforms.
In the wet-type supersonic non-destructive test method, the close contact between the test object 101 and the vibrator 106 makes it possible for the vibrator to receive stable and large wave forms even, when the pressing force of the supersonic vibrator is small.
However, additional treatments are necessary for the wet-type test method. Namely, it is necessary to apply the liquid contact medium 105 to the surface of the test object 101 prior to the test, and to eliminate the contact medium 105 after the test. This operation is not easy. Moreover, the contact medium 105 sometimes cannot be completely removed. In such case, contact medium 105 left on the test object 101 will make the test object 101 unclean, and it is possible to form rust on the test object 101.
An example of the dry-type supersonic non-destructive test method is shown by a cross-sectional diagram in FIG. 6. In the figure, the test object 101 including the upper and lower plates 102 and 103 is also prepared by spot welding. Then, the nugget diameter D of the welded part 104 is determined for confirming if the welding is firmly made.
In the dry-type method, a tube shaped body 112 with a bottom wall is provided on a free end of a supersonic vibrator 111. A free end 112a of the tube shaped body 112 is made of a flexible contact medium such as a thin rubber film. The space determined by the free end of the vibrator 111 and the tube shaped body 112 is filled with a liquid contact medium 113 such as water or oil as a supersonic propagation material. Accordingly, a supersonic sensor head 110 is structured. The test object is examined by closely applying the free end 112a of the tube shaped body 112 included in the supersonic sensor head 110. In the same way as in the wet-type method, a supersonic wave from the sensor head 110 goes forward and is reflected in the test object, so that the nugget diameter D is detected by the difference of forwarding and returning supersonic waveforms.
When the supersonic non-destructive apparatus shown in FIG. 6 is used, the free end 112a of the tube shaped body 112, which is made of the thin rubber film or the like, is largely deformed, and hence a contacting area between the free end 112a and the test object 101 changes. In accordance with the change of the surface area, the supersonic wave propagation area from the supersonic vibrator 111 to the test object 101 is also changed. Therefore, the test accuracy is affected. Moreover, it is difficult to maintain the durability of the free end 112a of the tube shaped body 112 made of a thin rubber film. Furthermore, it is not easy to fill the tube shaped body 112 with the liquid contact medium 113. As a result, working efficiency is not very good.
FIGS. 7A to 7C describe another example of the dry-type supersonic non-destructive test method. As shown in a cross section of FIG. 7A, the supersonic non-destructive test is also carried out by using a silicone rubber 122 which is a gel material with an excellent flexibility and restoration as a supersonic propagation material. The contact medium 121, as a supersonic propagation material, includes a silicone rubber 122 and a net 123 made of polypropylene with which the silicone rubber 122 is covered. The contact medium 121 is placed on the top surface of a test object 120. The contact medium 121 is interposed between a supersonic vibrator 124 and the test object 120. When the supersonic vibrator 124 is moved downwardly, the contact medium 121 is also pressed down. Therefore, the net 123 and the silicone rubber 122 are deformed. As a result, close contact is attained between the supersonic vibrator 124 and the contact medium 121, and between the contact medium 121 and the test object 120. In this state, the test object 120 is subjected to the supersonic non-destructive test by using the supersonic vibrator 124. After the test, the supersonic vibrator 124 is moved upwardly, and the contact medium 121 is brought back to have an original shape by the elastic restoring force of the silicone rubber 122 and the net 123, as shown in FIG. 7C (Japanese patent Kokai Publication 2002-181796).
Accordingly, the contact medium 121 is easily detached from the supersonic vibrator 124 and the test object 120. Moreover, the contact medium 121 can be repeatedly used because the net 123 provided on the silicone rubber 122 protects the surface thereof.
In this technology, however, a large cost is required for carrying out the test procedure. This is because the contact medium 121 has to be placed at a predetermined test position on a test object 120, and the contact medium 121 has to be collected after the test. Moreover, the contact medium 121 is largely deformed, so that a contacting area between the contact medium 121 and the test object 120 is changed. Accordingly, the supersonic wave propagation area from the supersonic vibrator 124 to the test object 120 is also changed. Therefore, the test accuracy is affected.
In addition to the above, it is possible that the net 123 on the silicone rubber 122 prevents the close contact between the supersonic vibrator 124 and the contact medium 121 and between the contact medium 121 and the test object 120. This could also affect the test accuracy.
FIGS. 8A to 8C describe a further example of the dry-type supersonic non-destructive test method. As shown in the figure, a silicone rubber 122 has a receiving part 112a which has a shape for tightly accepting a free end of a supersonic vibrator 124. The receiving part 112a of the silicone rubber 122 is in close contact with the corresponding surface of the supersonic vibrator 124. The outer surface of the silicone rubber which is not in contact with the vibrator 124 is covered with a net 123. On the other hand, the surfaces of the silicone rubber 122 and the vibrator 124 which are in contact with each other are not covered with the net 123, for maintaining the close contact.
When the supersonic vibrator 124 is operated to press the contact medium 121, the contact medium 121 is deformed as shown in FIG. 8B. Accordingly, the contact medium 121 closely contacts the test object 120. In this state, the supersonic test is carried out. When the supersonic vibrator 124 is raised up after the test, the contact medium 121 is raised up together with the vibrator 124.
The elastic restoration force of the silicone rubber 122 and the net 123 makes it possible to easily loose the close contact between the test object 120 and the contact medium 122 as shown in FIG. 8C (Refer to Japanese Kokai Patent Application 2002-181796).
Japanese Kokai Patent Application 2002-181796 (FIGS. 8A to 8C) discloses that the contact medium 121 in the supersonic non-destructive test apparatus is always maintained to have a close contact state with the free end of the supersonic vibrator 124. Therefore, it is possible to omit an operation for placing the contact medium 121 at an appropriate position between the contact medium 121 and the test object 120.
However, the contact area between the contact medium 121 and the test object 120 changes because the shape of the contact medium 121 is largely changed. Depending on the change of the contact area, the supersonic propagation area from the supersonic vibrator 124 to the test object 120 is widely changed. Accordingly, the test accuracy is affected by the change. Moreover, the net 123 covering the silicone rubber 122 prevent the contact medium 121 and the test object 120 from closely contacting with each other. This also will affect the test accuracy.